1. Field of the Invention
The present invention is generally in the field of power amplifiers. More specifically, the invention is in the field of power amplifier power detection.
2. Related Art
Various methods for detection the power output of a power amplifier are known. For example, in the coupler detector approach, a coupled line is electromagnetically coupled to a transmission line, and a detector circuit is connected to one node of the coupled line to detect the power output transmitted by a power amplifier along the transmission line.
A known problem with the coupler detector approach, however, is that harmonic signals can be generated by the detector circuit. These harmonic signals can be re-coupled onto the transmission line and introduce undesirable harmonic distortion into the transmission line, severely degrading the signal transmitted along the transmission line.
The conventional approach to reducing harmonic distortion in a coupler detector arrangement has been to provide a filter, such as a low pass filter, at the output node of the transmission line. This filter reduces the undesired harmonic signals generated by the detector circuit. However, the filter also adds loss to the signal path or “through path” along the transmission line. As a consequence, the efficiency of the power amplifier is significantly degraded, which is undesirable.
Accordingly, there is a strong need in the art for an efficient coupler detector circuit with reduced harmonic distortion. There is also a need in the art for a coupler detector circuit which does not reduce the efficiency of the power amplifier.